In Winchell et al. U.S. Pat. No. 4,177,905, a closure system for a threaded container is disclosed. A threaded closure cap has an annular skirt which engages a resilient gasket stretched over the bottle neck and overlying a cap support flange which extends radially outwardly from the neck. Downward axial movement of the cap relative to the container provides a vertical compressive force, pressing the resilient gasket against the cap support flange by the cap skirt for sealing.
However, it is of course of significant importance that the compressed gasket residing on the cap support flange should not slip outwardly to relieve its compression, which could possibly open pathways for the migration of contamination into the cap system between the neck of the container and the cap.
Furthermore, a typical cap support flange of a molded plastic closure for a container may contain a small parting line on its outer surface, which may comprise small ridges of plastic extending across the surface and being on the order of 0.005 cm. high or higher. This seemingly inconsequential ridge of plastic which may be formed at the parting line on the cap support flange may, in some circumstances contribute to a failure of a tight seal which can otherwise be formed through the use of the resilient gasket pressed between the cap support flange and the bottom of the closure cap.
By means of this invention, the above disadvantages of the prior art can be eliminated to provide a closure system seal of increased reliability at little increased cost.